1. Field of the Invention
The present invention relates to a stereoscopic endoscope enabling three-dimensional observation of a region to be observed.
2. Description of the Related Art
An endoscope system, of which an elongated insertional part can be inserted into a body cavity to observe a region to be examined that cannot be viewed directly, has been widely adopted. A standard endoscope system can merely visualize a region to be examined as a planar image providing no depth perception. It is therefore hard to observe fine irregularities on the surface of the wall of a body cavity, which makes it difficult to make diagnosis or give various kinds of treatment during observation under endoscopic guidance.
To overcome the foregoing drawback, a plurality of observation optical systems may be set in array. These observation optical systems are arranged so that the optical axes thereof will create an angle of convergence and thus have a parallax between them, thus permitting three-dimensional visualization of a region to be observed.
In this type of stereoscopic endoscope system disclosed in, for example, Japanese Patent Laid-Open No. 57-69839, a pair of image transmission optical systems are installed in an insertional part of an endoscope, a pair of objective optical systems are installed in distal parts of the image transmission optical systems, and a pair of eyepiece optical systems are installed in a proximal operational part of the endoscope. An angle of convergence created by the pair of objective optical systems is adjusted so that a region to be observed can be seen three-dimensionally.
FIG. 1 shows a schematic configuration of a conventional stereoscopic endoscope. A stereoscopic endoscope 51 has two objective lens arrays 52a and 52b, and two relay lens arrays 53a and 53b for transmitting images formed by the objective lens arrays 52a and 52b in the distal part of an elongated insertional part thereof. The respective images are picked up by solid-state imaging devices 54a and 54b that may be CCDs.
In a stereoscopic endoscope, if the right and left images formed by two optical systems are distorted even slightly, a plane region is seen waxing or waning. The visualized image can therefore not be said to have true three-dimensionality. For normal three-dimensional visualization, it is a must to prevent an optical system from distorting an image.
A rather wide-angle optical system is needed to recognize the location of a observed region in the whole of a subject. The wide-angle optical system cannot help causing distortion in the perimeter of an image from the designing and manufacturing viewpoints.
For normal three-dimensional visualization, it is required to prevent right and left optical systems from distorting images. In a stereoscopic endoscope having wide-angle optical systems, distortion occurs in the perimeters of images from the designing and manufacturing viewpoints. Thus, normal three-dimensional visualization has not yet been realized.
When an attempt is made to realize normal three-dimensional visualization, a wide-angle optical system cannot be employed. All observation images have therefore come to show narrow fields of view. When a wide-angle optical system is used to exhibit a wide field of view, normal three-dimensionality is unavailable because of distortion in the perimeters of observation images. This necessitates the use of a stereoscopic endoscope that can provide a rather wide-angle field of view which aids in recognition of the location of a region to be observed in the whole of a subject and permits normal three-dimensional visualization of an object region to be observed.
In the conventional stereoscopic endoscope shown in FIG. 1, when the distance to a subject changes, the angle of convergence varies. When a subject approaches, the angle of convergence becomes larger as indicated with a dashed line in FIG. 1 and the three-dimensionality improves. When the subject goes away, the three-dimensionality deteriorates. That is to say, three-dimensionality varies depending on the distance to a subject.
For example, when a stereoscopic endoscope is employed for a surgical procedure, a surgeon wants to proceed with the procedure while having the same sense of three-dimensionality irrelevant of whether he/she observes a region to be examined at a near point or a far point. The aforesaid stereoscopic endoscope, in which three-dimensionality improves at a near point but deteriorates at a far point, cannot satisfy the foregoing demand from surgeons.
As mentioned above, in the conventional stereoscopic endoscope, the angle of convergence varies depending on the distance to a subject and the three-dimensionality of a produced image changes. Observation cannot therefore be carried on with the same sense of three-dimensionality.
In contrast, it is also demanded to observe a subject with a sense of three-dimensionality that ensures comfortable seeing and differs between a near point and a far point. In the past, it has also been difficult to control three-dimensionality and thus provide a desired sense of three-dimensionality for a certain distance to an object.
As described above, a stereoscopic endoscope should be able to control three-dimensionality optimally according to a distance to a subject and a position in a field of view, and visualize an intended region to be observed normally and three-dimensionally while exerting the desired three-dimensionality. The conventional configuration can hardly realize such a stereoscopic endoscope.